Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVENTION
During service or as a result of well operations, casing failures have oc-
curred. One repair technique for such failures has been to remove that portion
of
the casing above the break and insert new casing with what has been referred
to
15 as a casing patch at the lower end. The casing patch goes over the top end
of the
remaining casing in .the well. "Casing" as used herein -includes any- tubular
used - - -
downhole. In general, prior casing patches have offered a seal of one type or
another in conjunction with.a gripping-member to hold the casing patch
together. -
In some designs the sealing material has been lead. Such products have been
20 offered by Baker Oil Tools under Product Nos. 160-21, 162-20, and 163-20.
Other designs have used opposed chevron seals in what is known as. a high pres
sure pack-off assembly such as that sold by Baker Oil Tools under Product No.
I IO-59. This accessory allows latching onto a fish and thereafter applying
pres
sure. Blades are provided at the lower end to facilitate acquisition of the
fish by
2~ milling the jagged top of the fish free of surface irregularities.
The designs involving the use of lead have created excessive radial forces
-on the casing patch body or the casing itself against which the seal is
desired. In
1
CA 02198163 2002-11-29
some cases the body has ballooned outward due to the inner pressure or in
others the
casing itself has collapsed. Some of these designs are not releasable.
Releasable casing patches have previously been offered by Bowen Tools in its
packer-type tubing and casing patches. This design has featured a spiral wound
S grapple design which allows disengagement from the fish if a seal is not
created for
any reason. The Bowen design has used a large rubber ring as the sealing
element. In
view of the environment in which these casing patches must be inserted, a
limited
space is available which has resulted in thinning the wall in the Bowen design
to
accommodate the presence of the rubber seal ring The thirming of the wall in
an effort
to control the outside diameter of the casing patch in turn has resulted in a.
low burst
pressure rating for this particular design. Other designs, such as the Baker
Oil Tools'
High Pressure Pack-Off*, require the use of fairly thick packing which in turn
reduces
the available wall thickness around the packing and reduces the pressure
limits of the
joint. Other designs of casing patches, such as those made by Gotco
International, Inc.
use individual elastomer rings inserted into the patch body in separate
grooves. This
design allows for extrusion gaps due to irregularities in the casing
dimensions,
thereby limiting, its ability to retain pressure once the joint is assembled.
Typically, casing, once exposed in the wellbore, can have pitting corrosion or
general deterioration of its outer surface. The prior designs of patches were
required
2U to seal this uneven surface. In prior applications, a service company would
run a
dressing tool that simply created a top bevel on the casing to facilitate
insertion of the
patch over the top of the casing and to reduce the potential for damage to the
seal on
the casing patch during insertion. While such tools produced the desired top
bevel,
below that the lower portion of the mill would gouge and severely scratch the
casing
outside surface. This in turn reduced the surface quality
* Trade-mark
2
219$163
for the seal which caused leaks of the patch under pressure. The. tolerance of
casing outside diameter is governed by the American Petroleum Institute which
states that casing outside diameter can vary +1% to - .S%. Therefore, for a
95/s"
nominal outside diameter casing, the diameter can be as much as .096 inch
oversize
to as little as .048 inch undersize. Prior casing patches that use chevron or
V-type
packing have been less than effective due to the large variances in
dimensions.
Accordingly,- the present apparatus and method have as their objective to
properly prepare the outer surface of the casing stub in the wellbore prior to
insertion of the casing patch. With the outer surface of the stub prepared,
another
objective is to provide a casing patch using one or more fins which can flex
as the
joint is put together an provide an adequate seal for the casing. Another
objective
is to improve the seal obtained in the casing patch by combining the use of
one or
more fins for extrusion barriers in combination with any elastomeric or rubber
sealing component which can be significantly thinner than prior designs-that
lacked
extrusion barriers to- allow for less reduction in wall for accommodation of
the seal.
It is a further objective to accommodate the irregularities of the casing by
using a
series of fins at different diameters to compensate for such dimensional
variations.
Another objective is to provide a dressing tool for the stub portion of the
casing in
the wellbore which can adequately prepare the outer surface of the stub, in
place,
to facilitate the reliability of the casing patch, whether.using one or. more
fins or
in conjunction with one or more resilient seals.
SUMMARY OF THE INVENTION
A casing patch is disclosed which uses one or more fins which elastically
flex to accept a casing stub. The casing stub is prepared with a dressing tool
containing a special mill to obtain the requisite finish on its outer surface
prior to
3
CA 02198163 1999-OS-19
insertion of the casing patch. The flexible fin or ~.ns provide a metal-to-
metal seal to the outer surface of the casing patch and a grip assembly
holds the joint together. In certain applications, the fins can be combined
with a resilient seal where the fins preferably provide a complete
extrusion barrier to the resilient seals. Using the fins, which preferably
are integral to the body, alone or in combination with a resilient seal or
seals, the wall thickness of the joint can be maintained at thicker values
for a given size as compared to prior designs, thus, ensuring a sufficient
pressure rating for the joint which is at least equal to the rating of the
casing stub.
Accordingly, in one aspect of the present invention there is
provided a casing patch apparatus for connecting on to a stub casing in a
wellbore comprising:
a tubular body having an opening large enough to pass over
the stub;
a seal assembly comprising at least one cantilevered fin
mounted within said body, said fin deflected as said body is advanced over
the stub, said fin providing a metal-to-meal seal between said body and
the stub.
According to another aspect of the present invention there is
provided a method of preparing a downhole casing tubular comprising:
using a dressing tool to polish the exterior surface of a casing
stub in the wellbore;
connecting a casing patch housing to a string and lowering it
to the stub;
providing at least one cantilevered metal fin around the
inside said housing;
lowering an open end of said housing over the stub;
providing a metal-to-metal seal as said fin contacts all around
the polished portion of the stub;
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CA 02198163 1999-OS-19
securing the housing to the stub.
BRIEF DESCRIPTION OF THE DRAWING
Embodiments of the present invention will now be described
S more fully with reference to the accompanying drawings in which:
Figure 1 is a schematic sectional elevational view of the
casing patch fully assembled.
Figure 2 is a sectional elevational view showing the
embodiment that combines the ins with the elastomeric seal.
Figure 3 is a detail of the circle labelled "3" on Figure 2
showing in greater detail the resilient seal and how it is situated adjacent
the fin structure.
Figure 4 is a part section view of the body of the casing patch
illustrating the shape and initial orientation of one of the fins.
Figure 5 is an alternative shape for one of the fins shown in
section.
Figure 6 is the sectional representation of the dressing tool
for the stub portion of the casing prior to assembling the casing patch.
Figure 7 is a side view of the gauge mill blade in the tool
depicted in Figure 6.
Figure 8 is a front view of the blade shown in Figure 7.
-4a-
2198163
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT -
The casing patch C- is- illustrated schematically in -Figure -1. It has a body
with a thread 12 to allow engagement to the newly run casing 14. Body IO has
a seal area 16 and a slip or gripping area 18. The body 10 goes over the old
5 casing stub 20 which is shown in cross-hatch in Figure 1. The slip area 18
encompasses any one of several known gripping techniques which are activated
by
a longitudinal force applied to the new casing 14 from the surface. The seal
area
16 seals the joint so that pressures internal to the joint in flow path 22 do
not
escape out through the annular space 24 formed between the old casing 20 and
the
10 body 10.
Figures 2, 3, and 4 are helpful in better seeing the details of the seal area
16.
Figure 2 is a section view showing in more detail the seal area i6. Detail "3"
of
Figure 2, which is shown in 'magnification in: Figure 3; 'illustrates the use
of a - --.
plurality of circular ribs 26. Figure 3 is a- partial view showing-two such-
ribs 26.
Note that one or more ribs are within the purview of the invention. In between
the - -
ribs 26 is a resilient seal 28.. The use of the resilient seal-is optional.
Where the
thermal conditions and- chemical compatibility conditions permit and
additional - -
sealing capability is required, resilient-seals, such as 28; cawbe used in
conjunction
with the fins 26. In order to manufacture the casing -patch -seal-of the
present -- ~ - --
invention in conjunction with a resilient seal, such as 28, the entire space
between
adjacent fins 26 is filled with the material. Subsequently, a notch 30 is cut
out to
leave a generally V-shaped top 32 to the resilient sealing element. The
remaining
top portion 34 is not necessary to effectuate the seal. In essence; the fins
26 act
as extrusion barriers to the resilient sealing element 28. With the aid of the
extru-
sion barrier that spans the gap to the old stub casing 20 (see Figure 1), the
thick-
ness of the sealing element can be reduced as compared to prior designs that
did
2198163
not rely on any extrusion barrier. Thus, the thickness of the wall 36 (see
Figure
4) in the area of the ribs 26 need not be reduced to accommodate the thickness
of
the sealing element 28. As better shown in Figure 2, the wall thickness
represented -
by arrow 38 is very close to the wall thickness 40 immediately above. As an
example, the internal diameter above the fin area 26 is shown in Figure 2 and
above transition 42 can be 7.734 inches while just below the transition, the
diame-
ter is 7.875 inches, all dimensions being within normal tolerances for the
applica- -
tion.
Figure 4 shows the details of a specific fin 26. It is preferably integral to
the body 10, but can also be a separate unit. It has a generally tapered form
with
an upper included angle 44, preferably about 55° from vertical (an
acute included -
angle), and a lower angle 46 shown in Figure 4 to be preferably about 4~
° from
vertical. As a result; closer to wall 36 the cross-section of the din 26 is
greater-
than it is at the tip 48:- Other included angle orientations are possible or
even --
different angles in a given stack of-fins. The seal assemblies need not all be
identical. Some can have reverse orientations to others so that the fins 26
can, in _
conjunction with said seal assemblies 28; function in two opposite directions
to- -
hold pressure. Thus; in the areas of-greater-stress concentration, the fins 26
have
a greater cross-sectional area to facilitate their flexure elastically to
accept the old
casing 20. - The inside diameter defined by the tips 48 of each of the fins 26
need
not be identical. Referring to Figure 2, the fins 26 closer to transition 42
can have
a slightly smaller internal diameter measured at the tips 48 than the
remaining fins
further down which are closer. to the thread 50 which supports the slip area
18 -
shown in Figure 1. Again, those skilled in the art will appreciate that the
slip area
18 is intended to schematically represent a known gripping device. In the
preferred
embodiment, a releasable gripping device of known design, such as illustrated
in
6
Zl9Bi.63
the Bowen tool, is acceptable for service in the casing patch C of the present
invention. __-
In order to-obtain a reliable seal using just one or more fins 26, surface
preparation of the old casing 20 is helpful. The dressing tool illustrated in
Figure
6 is used to adequately prepare the old casing 20 prior to advancing the body
IO
over it. The dressing tool of Figure 6 has a body 52 which houses a lower mill
54.
The lower mill 54 slips over the old casing 20, shown in dashed lines in
Figure 6
when it is inside the body 52. The lower mill 54 is intended to knock off
scale
and other external contamination_and is generally formed-by a coating of a
brazing
material with tungsten-carbide chunks, known as SUPERLOY~ when sold by
Baker Oil Tools. As the-body 52 advances over the oId casing stub 20, it comes
in contact with stabilizer pads 56. The stabilizer pads are again internal to
the
body 52 and are disposed around its periphery adjacent to the gauge mill 58.
.The
gauge mill is a series of blades within the body 52 and away from its lower
end.
An end view of one-biade is shown in Figure 7 and a front -view is shown in
Figure 8. As shown-in Figure 8, a single column of inserts 60 is used on a
partic-
ular blade 62. The inserts are brazed xo the blade 62 with a known brazing
materi-
al which can also have chucks of tungsten-carbide in it. The inserts or
buttons 60
have a semi-circular cross-section as shown in the end view of Figure 7. Near
the
top, the preferred shape is rectangular in cross=section. As shown in Figure
8,
inserts 60 have a slight taper to them and present a relatively continuous
cutting
line 66. A series of such blades 62 can be used. In conjunction with the
stabilizer
pads 56, the blades 62 can deliver an external surface on the old casing 20
which
is a 63 Micron finish, which is normally only attainable in a machine shop and
has
heretofore been unattainable with known dressing tools. As the dressing tool
of
Figure 6 further advances, the old casing stub 20 encounters a bevel 68 which
puts
7
CA 02198163 2002-11-29
an external bevel on the top of the old casing 20 and a reverse bevel 70 which
puts an
internal bevel on the top of the old casing 20. The old casing 20 then has an
internal
and external bevel which comes to a point, thus facilitating the insertion of
the body
of the casing patch C of the present invention. The gauge mill 58 works akin
to the
5 well known Baker Oil Tools line of metal munches milling products which
employ
tungsten-carbide inserts in a row or a column as described in U.S. Patent Nos.
4,796,709 and 5,456,312. After the dressing tool of Figure 6 has been properly
employed, the casing patch C can be advanced over the old casing 20 and the
slip area
18 engaged to complete the joint. As the body 10 is advanced over the old
casing 20,
10 the tips 48 of fins 26 flex upwardly and ride along the uow polished outer
surface of
the old casing 20. As previously stated, since in the prefe~-r~d embodiment
some of the
fms will have a larger inside diameter toward the thread 50 than the
transition 42, any
dimensional irregularities (such as a slight out of roundtless) that are still
present on
the outer surface of the old casing 2() after use of the dressing tool will
not make a
difference as one or more of the ribs or fins 26 come into all around metal-to-
metal
contact with the outer surface of the old casing 20. The fins 26 are stressed
when in
contact with the casing stub 20 to ensure good metal to metal contact. Thus,
in one
embodiment, particularly where high temperatures are expected, and resilient
materials are not suitable, the casing patch C makes a metal-to-metal seal
with one or
2(I more of the ribs 26, which are in an interference fit with the old casing
20. The slips
or grapple mechanisms 18 hold the casing patch C to the old casing 20.
Alternatively,
if the fins 26 are used in conjunction with a resilient seal 28, which can be
rubber or
plastic or other man made or naturally occurring material suitable for the
application,
the fins 26 again span the potential extrusion gap between the body 10 and the
old
casing 20. With
8
2198163
the support lent by the fins 26, the sealing elements which have a generally
chev-
ron-type appearance when observed in cross-section, as shown in Figure 3, func-
tion as a back-up to the metal-to-metal seal provided by the fingers or fins
26.
It can be seen from Figure 3 that the lower end 72 of a particular resilient
seal 28
is generally V-shaped conforming generally to the V-shape upper end 32. As a
result, the seal 28 functions akin to a chevron seal. The chevron-shaped seals
28
can be aligned or some can be inverted for sealing in both directions.
However,
with the polishing, which has already initially occurred using the dressing
tool, and
the fins 26 acting as back-up, the required radial thickness of the seal 28 is
re-
duced such that for a fin having a seal inside diameter of about 7.506 inches,
the
thickness of the seal 28 is about .185 inches as compared to a fin 26 having
an
inside diameter of 7.566 inches where the thickness of the seal 28 is .155
inches.
These relative dimensions are an example of an installation for 75/s inch 39
casing:
Figure 5 illustrates an alternative shape for the fin 26: It has a thick base
74 going into a generally tapered body 76 and a blunt tip 78. Using known
stress -
analysis techniques, other shapes can be used without departing from the
spirit of
the invention. Once the anticipated amount of .flexure is known, as well as
the
pressure differential limits during service, known stress analysis techniques
can be
used to define a variety of shapes which will flex to bridge the gap-to allow
the -- -
body 10 to slip over the old casing 20 without the fins 26 being pushed so far
back
that the effectiveness of bridging the gap disappears.On the other hand, the
preferred upper included angle 44 is kept in the range of about SS ° in
the preferred
embodiment, although other angles could be used so as to optimize the ability
of
the fins to resist differential pressure in one or two opposite directions
once the
casing patch C is assembled.
9
2198163
Those skilled in the art can see that the use of one or more flexing fins 26
can result in a casing patch C which seals on a metal-to-metal basis. With the
variety of internal diameters on a series of fins 26, as measured at the tips
48, any
surface imperfections, even after dressing, can be accommodated by one or more
of the fins 26. Should additional sealing capability be desired, the sealing
element,
such as 28, can be used. In the preferred embodiment having a generally
chevron-
like shape; the thickness of such seals 28-is-fairly small since the adjacent
fin 26
effectively bridges the extrusion gap. As previously described, alternative
shapes
of cantilevered structures can serve as the fins 26 while different shapes and
materials can be used for the resilient seal 28, all without departing from
the spirit
of the invention. The resilient seal 28 can be bonded to the body 10. The
tool,
when run with known overshots, can be releasably secured to the old casing 20
so
that, if for any reason, the integrity of the seal is jeopardized, the ,casing
patch C
can be removed without having to cut the casing to get it out.
With the design as described; the pressure rating of the joint is at least
equal to the pressure rating of the old casing 20. The ability to provide a
metal-
to-metal seal using the fins 26 is facilitated by the dressing tool which uses
in
combination the stabilizers 56, which are a plurality of internal projections,
to ---- ---- -
support and properly center-the pipe while the blades 62 with inserts 60
provide a
smooth finish in the order of about 63 Microns.
The foregoing disclosure and description of the invention are illustrative and
explanatory thereof, and various changes in the size, shape and materials, as
well
as in the details of the illustrated construction, may be ,made without
departing
from the spirit of the invention.
sr~bakcc~4d3~ptokasingpatch.app sg
1
